Mercury - Quicksilver Relay Assembly Electrical System Marine-Grade Construction 882751A04. Overview. Every boater knows the feeling of turning the key and waiting for that familiar hum - that moment when the engine wakes up and you instantly know the day is going to go right. Reliable electrical parts make that moment possible, and this Mercury Marine part is one of those quiet heroes that keeps your whole system breathing steady. A dependable relay is something you rarely think about when it w